In general, various types of electronic apparatuses include respective batteries and are driven using power stored in the batteries. In an electronic apparatus, a battery may be replaced or recharged. To this end, the electronic device includes a contact terminal for contact with an external charging device. That is, the electronic apparatus is electrically connected to a charging device through a contact terminal. However, the contract terminal of the electronic apparatus is externally exposed and thus may be contaminated by foreign materials or short-circuited by moisture. In this case, contact failure occurs between the contact terminal and the charging device and thus the battery of the electronic apparatus is not charged.
In order to solve the above-described problem, wireless power transfer (WPT) for wirelessly charging the electronic apparatus is proposed. A WPT system transfers power over the air without a wire, thereby maximizing convenience of supply of power to a mobile apparatuses and digital appliances.
A WPT system has advantages such as energy conservation through real-time power use control, overcoming of power supply space restriction, and reduction in number of used batteries through battery recharging.
Representative examples of a method of implementing a WPT system include a magnetic induction method and a magnetic resonance method. The magnetic induction method uses a non-contact energy transmission technology for providing two coils close to each other and generating electromotive force in the other coil by magnetic flux generated when current flows in one coil, and may use a frequency of several hundred kHz. The magnetic resonance method uses a magnetic resonance technology of using only an electric field or a magnetic field without an electromagnetic wave or current, has a power transfer distance of more than several of meters, and may use a band of several MHz.
A WPT system includes a transfer device for wirelessly transferring power and a reception device for receiving power and charging a load such as a battery. At this time, a transfer device capable of selecting the charging method of the reception device, that is, any one of the magnetic induction method and the magnetic resonance method, and wirelessly transferring power in correspondence with the charging method of the reception device has been developed.
Meanwhile, as the reception device provided in the charging region of the transfer device is intentionally shaken or is frequently shaken as in a vehicle, a coupling coefficient is rapidly changed due to misalignment between the transmission and reception devices and thus power transferred from the transfer device is rapidly changed, thereby damaging the reception device.